Commercial processes for producing adiponitrile, an important intermediate in the manufacture of nylon-6,6 and related products, typically include a stage in which 3-pentenenitrile (or 4-pentenenitrile) is hydrocyanated in the presence of a nickel (0) catalyst to form adiponitrile. It is known that cis-2-pentenenitrile is formed as a byproduct during such a hydrocyanation. The formation of cis-2-pentenenitrile represents an adiponitrile yield loss in the process. Furthermore, the accumulation of cis-2-pentenenitrile during the hydrocyanation reaction is undesirable because it behaves as a catalyst poison. However, the removal of cis-2-pentenenitrile is not straightforward. It can be separated from unreacted 3-pentenenitrile by distillation. Alternatively, it can be removed by reaction with an alkali metal sulfite and bisulfite solution but this can complicate the procedure. With this in mind, rather than physically removing the cis-2-pentenenitrile, efforts have focused on converting it to a useful product. In this regard, it is preferred to isomerize cis-2-pentenenitrile to 3-pentenenitrile, which can then be recycled back into the hydrocyanation reaction.
The isomerization of cis-2-pentenenitrile to 3-pentenenitrile has been described in U.S. Pat. No. 3,526,654 and U.S. Patent Publication No. 2006/0194979. Both describe that the isomerization reaction may be carried out in the presence of an aluminium oxide catalyst. In U.S. Pat. No. 3,526,654, the aluminium oxide catalyst used is Alcoa F-1, while in U.S. Patent Publication No. 2006/0194979, the aluminium oxide catalyst has a BET surface area of at least 50 m2/g.